The general field of technology to which the present invention belongs is wafer manufacture and substrate processing equipment.
Wafers or substrates with exemplary characteristics must first be formed prior to the formation of circuit devices. In determining the quality of the semiconductor wafer, the flatness of the wafer is a critical parameter to customers since wafer flatness has a direct impact on the subsequent use and quality of semiconductor chips diced from the wafer. Hence, it is desirable to produce wafers having as near a planar surface as possible by utilizing polishing and grinding apparatus.
In a current practice, cylindrical boules of single-crystal silicon are formed, such as by Czochralski (CZ) growth process. The boules typically range from 100 to 300 millimeters in diameter. These boules are cut with an internal diameter (ID) saw or a wire saw into disc-shaped wafers approximately one millimeter (mm) thick. The wire saw reduces the kerf loss and permits many wafers to be cut simultaneously. However, the use of these saws results in undesirable waviness of the surfaces of the wafer. For example, the topography of the front surface of a wafer may vary by as much as 1-2 microns (xcexc) as a result of the natural distortions or warpage of the wafer as well as the variations in the thickness of the wafer across its surface. It is not unusual for the amplitude of the waves in each surface of a wafer to exceed fifteen (15) micrometers. The surfaces need to be made more planar (planarized) before they can be polished, coated or subjected to other processes.
Current substrate polishing technology uses chemical slurry to aid in polishing a substrate. Means for delivering the slurry onto the polishing plate vary for typical chemical mechanical polishing (CMP) techniques. A supplemental alkaline stream is commonly used in addition to the chemical slurry to enhance substrate removal rates during polishing. Unfortunately, one negative side effect of this alkaline stream is that it raises the pH level of the mixture to a level beyond the stability threshold of the silica solution. As a result, colloidal silica particles agglomerate and fall out of the suspension. The particles tend to scratch the wafer during polishing, and in general reduce polishing effectiveness. Hence, improvements are desired to the typical prior art processes.
Additional deficiencies in the current art, and improvements in the present invention, are described below and will be recognized by those skilled in the art.
In one embodiment of the invention, a manifold for mixing chemistries is provided comprising a plurality of inlets coupled to a manifold interior chamber with each inlet adapted to be coupled to a chemistry line, a mixing element within the chamber, and an outlet coupled to a wafer polishing platen.
The mixing element can take a variety of forms. For example, the mixing element can be shaped, at least partially, in a generally cork screw shape. Furthermore, the mixing element can be a static mixing element. Similarly, an agitator can be used to move the mixing element so as to agitate the mixing element to mix the chemicals.
By injecting the various chemicals into a mixing manifold for near immediate use and delivery to the polishing plate, the present invention reduces or minimizes the time that the chemicals are interacting. As a result, the present invention lessens the time toward instability, which would otherwise occur in the slurry solution.
Other features of the embodiments of the invention will become more fully apparent from the following detailed description, the appended claims, and the accompanying drawings.